1. Field of the Invention
The present invention relates generally to controlling the admission of new connections to a packet-based switch. More specifically, the present invention relates to an adjustable connection admission control system for a packet-based switch.
2. Description of the Related Art
FIG. 1 is a schematic view of a conventional packet-based switching system. In FIG. 1, traffic flows from left to right. The interfaces IF1 through IF4 are represented on both the left and right side of a switching matrix. The left interfaces show traffic entering the switching matrix, and the right interfaces show traffic exiting the switching matrix. A user supplies traffic to an interface on the left and takes traffic from an interface (the same interface) on the right. The user may contract for the type of connection needed. For example, the user may contract for a constant bit rate (“CBR”) connection, a variable bit rate (“VBR”) connection or an unspecified bit rate (“UBR”) connection. The user might provide traffic information such as a sustained cell rate, a peak cell rate, a maximum burst size, etc. This traffic information provides the switch with information regarding the maximum bounds for the user's traffic. However, it would be unusual for all users to operate at the maximum bounds. The traffic rate is expected to be bursty and somewhat unpredictable, and the switch can accommodate all traffic that fits with the maximum bounds defined by the traffic information. This presents a problem in resource allocation. That is, it is difficult to determine how many connections can be handled by a switch when the traffic rate of each connection is variable.
One way to address the resource allocation problem is for the switch to assign a nominal bit rate to each requested connection. The number of permissible connections is determined from the nominal bit rate using a connection admission control (also referred to as “CAC”) system. CAC must be done for each point of possible congestion. In FIG. 1, the circles represent the points of possible congestion, where connection admission control is used. In general, CAC is done at each egress points. For example, if all users connected to interface 1 transmit at their maximum permissible rate, there may be congestion in the link carrying traffic from interface 1 to the switching matrix. Conventional connection admission control is described in U.S. Pat. Nos. 5,949,757; 5,936,958; 5,751,691; 5,696,764; 5,583,857; 5,555,265 and 5,341,366, which are hereby incorporated by reference.
Connection admission control is based on traffic descriptors such as peak cell rate, sustained cell rate, maximum burst size, cell delay variation tolerance, etc. The CAC mechanism allocates the minimum switch resources necessary to meet the requirements of the requested connection. If sufficient resources are not available, CAC will not complete the connection. Connection admission control is done in different ways for different traffic classes (also referred to herein as different connection types). That is, constant bit rate, variable bit rate and unspecified bit rate connections are treated differently. For non-constant bit rate service, CAC provides statistical multiplexing. Bandwidth for variable bit rate connections is allocated by determining an equivalent bandwidth (“EBW”) based on the peak cell rate sustained cell rate and maximum burst size. EBW is also determined based on the link between the switch components being considered. For the link, parameters such as link speed, buffer size, buffer read out rate, and buffer structure (shared or individual) are considered.
To allocate bandwidth for the significantly different types of traffic, connection admission control requires complex mathematical manipulation of data. To provide superior service, it is desirable to allocate resources conservatively. On the other hand, to accommodate more users, it is desirable to allocate resources aggressively. Different switch operators desire a more or less aggressive approach to resource allocation. However, connection admission control is determined in advance by the switch manufacturer. Because of the complexities associated with connection admission control, it cannot be altered by the individual switch operator.